The present invention is generally related to communication networks including wireless telephony communication networks, communicating voice and data calls between an originating network and a terminating network, and more particularly to a communication network having dissimilar compression and decompression equipment, such as codecs, in the communication networks.
Communication networks, including wireless communication networks, typically include an originating network, a terminating network, and a communication link exchanging voice and data between these networks. In the case of telephony networks, analog speech signals are typically digitized through digital sampling prior to transmission over the communication link and then converted back to analog at the terminating network. To increase the capacity of the communication network, these digitized voice calls routed over the communication link are typically compressed through the use of compression and decompression equipment, commonly referred to as codecs, vocoders or transcoders. Typically, a codec resides at both the originating end and at the terminating end of a call, whereby the digitized voice is compressed by an encoding algorithm in a forward direction, and decompressed by a decoding algorithm at the receiving end. Other codecs may be utilized at other nodes of the communication network for a single call or data transmission. The decompressed voice signal is ultimately converted back to voice through the use of a digital to analog (D/A) converter.
Decompressed digitized voice signals are typically routed over a communication link, such as a public switched telephone network (PSTN) in a pulse code modulated (PCM) format, typically at 64 kbps. A compressed signal may have a rate of between 6 and 20 kbps, for example, in a GSM (Global System for Mobile Communications.) The rate of the air interface is usually lower than 64 kbps. In cellular networks utilizing xe2x80x9cvoice over IP (Internet Protocol),xe2x80x9d codecs may be positioned in gateways at the edge of the network, resulting in transmission at lower rates as far as possible
A number of different codec types exist today. For example, in GSM there are eight types available, with more being developed. Considering the wide range of codec variety, it is likely that a gateway may not support all codec types, and therefore there may be a mismatch between the codec in the mobile station and the gateway. A mismatch may result in a downgraded codec type in a gateway being selected, as compared to the mobile station codec type, causing poor speech quality. There is desired a communication system and method for effectively selecting a gateway when mismatches in codec types exist, improving signal quality.
The present invention achieves technical advantages as a system and method of selecting a gateway having a codec of the same type as the subscriber codec type or best adapted for the subscriber codec type, preventing unnecessary degradation of the voice signal. A communications system serving subscribers having an originating network in communication with a terminating network via a core network is disclosed. The core network includes a plurality of gateways, with each gateway adapted to route calls therebetween. Each gateway has at least one codec, and the communications system includes a network node for processing call requests from the subscribers having a particular codec type. The gateways are ranked based on the gateway codec availability, and the core network is adapted to route a voice call as a function of the gateway ranking.
Also disclosed is a method of communicating an encoded signal representative of speech across a core network between a subscriber served by an originating network including an encoder having an encoding algorithm and a terminating network. The core network includes a plurality of gateways, each having at least one resident codec. The method includes the steps of the subscriber sending a call request and the subscriber""s codec type to a first node within the core network, and the first node selecting one of several gateways in the core network as a function of the codecs available at the various gateways of the network.
Further disclosed is a method of communicating an encoded signal representative of speech across a core network between a subscriber served by an originating network including an encoder having an encoding algorithm and a terminating network. The core network includes a plurality of gateways, each gateway having at least one resident codec. The method includes the steps of the subscriber sending a call request and the subscriber""s codec type to a Mobile Switching Center (MSC) server within the core network. The MSC server consults a node within the core network for information indicative of available gateways in the core network. The MSC server selects one of several gateways in the core network as a function of the codecs available at the various gateways and the subscriber profile.
The present invention provides several advantages. First, the quality of a voice signal is improved by selecting a gateway having the best possible codec available for the mobile station codec. Second, a cost savings may be realized by transmitting a call for as long as possible over an IP network rather than over a traditional land-based network. Furthermore, subscribers who are willing to pay a premium for superior quality calls in accordance with the present invention are given the ability to do so. Also, the communications system efficiency is improved by having codec types at gateways matched, when possible, with the codec type of the subscribers. Some signaling in the communications system may be eliminated in accordance with the present invention, because gateway negotiation is decreased.